The solution conformation of two cell-differentiation pentapeptide fragments will be determined using high-resolution NMR techniques. These peptides are the active fragments of the thymic hormone, thymopoietin, that induces selective differentiation of T-lymphocytes, and the immunopoietic polypeptide, ubiquitin, that induces non-specifically both T and B cell differentiation. A parellel objective of this investigation is the development and application of NMR methods that are useful in the delineation of peptide conformations in general. Determination of the conformation of the cell differentiating fragments, and of their agonist and antagonist analogs is an essential prerequisite in delineating the conformation-activity relationships of these fragments. In addition to conventional NMR methods, we propose to employ nuclear Overhauser effect experiments, measurement of amide hydrogen exchange rates, 13C NMR studies, 2-dimensional NMR and metal binding studies using paramagnetic shift and relaxation probes.